Switch bank



Oct. 20, 1936.

R. W. WAGNER SWITCH BANK Filed Aug. 1, 1955 INVENTOR.

RALPH w. ,WAGNER A TTORNEY.

Patented Oct. 20, 1936 i "2,057,865 swrrcn BANK PATENT: OFFICE Ralph W. Wagner, Chicago, Ill., assignor to Associated Electric Laboratories, Inc., a corporation of Delaware Application August 1, 1935, Serial No. 34,176

-; 3 Claims; (Cl.---306) The present invention relates in general to switch banks, in particular to the-banks of selector and connector switches of the type commonly used in automatic telephone systems; and. the object of the invention is to produce a switch bank of this character which is better adapted for use with large capacity switches than those hitherto available.

The common Strowger switch bank is well "known, and is described and illustrated for ex ample in a book entitled Automatic Switching and Auxiliary Equipment by Kempster B. Miller. This bank comprises a plurality of so-called levels of contacts, in which the contacts are arranged" 'in semi-circularrows. Each level of the bank comprises two rows of radially spaced contacts separated by a thin sheet of insulation. The switch wipers are arranged in pairs. In the operation of a switch the wipers are first raised to a desired level and are then rotated in on such level, one wiper engaging the contacts of one row and the other wiper the contacts of the other row.

Now the wipers are constructed of springy material and are tensioned toward each other so as to secure good engagement with the bank contacts. As the wipers are rotated over the radially spaced contacts, therefore, they have to proceed by alternately separating and approaching each other, the separations occurring as the wipers ride up on successive pairs of contacts and the opposite movements taking place as the wipers pass the spaces between pairs of contacts. In other words, each wiper has to ride over an irregular surface formed partly by the contacts of a row and partly by the layer of insulation which separates this row from the other row of the level.

The operating conditions above pointed out give rise to what is known as wiper friction, which is a resistance that has to be overcome in rotation of the wipers. This resistance is a force to be reckoned with in both the setting and restoration of the switch. In the restoring operation the wipers are rotated backward by spring tension, which must be suflicient to overcome the wiper friction. In setting the switch, which is done by a stepping magnet, the. magnet has to be powerful enough to overcome the wiper friction and also to store tension in the restoring spring.

These considerations show that wiper friction is an important factor tending to interfere with the proper operation of switches of this character. It may be stated, however, that no particular trouble has been encountered in the past because the number of wiper sets on each switch has generally been limited to one set, although some times two sets have been used. With no more than two sets of wipers the overcoming of wiper friction is not beyond the capabilities of the standard restoring springs and driving magnets which are designed for switches using a single set of wipers. Recently, however, switches have been designed requiring from four to six sets off wipers. With such a large number of wiper sets; the wiper friction is increased to such an extent that it becomes a difiicult problem to deal with.

The obvious way of solving this problem is to provide stiffer restoring springs and 'more powerful driving magnets, and this solution is practicable, but it is open to the objection that the stand, ard springs and magnets cannot be used and new parts to perform the restoring and driving functions have to be designed and manufactured, all at considerable expense to the manufacturer.

The present invention solves the problem in a different way. Instead of increasing the power to overcome the increased wiper friction in a large capacity switch, the present invention goes to the root of the trouble and substantially eliminates the wiper friction. This makes it possible to successfully operate a switch having six sets of wipers with the ordinary driving magnet and restoring spring. In carrying out the invention two comb-shaped fillers or inserts are provided for each level of contacts, the said fillers lying one on each side of the strip of insulation which separates the two rows of contacts, and the teeth or projections on each filler occupying the spaces between the contacts of a row. Thus each wiper is provided with a level surface to ride over, made up of contacts and the interspersed teeth of the filler.

The invention is illustrated in the accompanying drawing, in which Fig. 1 is a top or plan view of a switch bank embodying the invention, Fig. 2 is a top view of one of the fillers or inserts, while Fig. 3 is a cross section of the bank on the line 3-3, Fig. 1.

Referring to the drawing, l and 2 are the clamping plates, which are held together by means of bolts 4. Between these clamping plates the various elements of the complete bank are firmly held to form a rigid structure.

As seen in Fig. 3, there are ten levels. These levels are all alike, so an explanation of the upper level will suffice to describe the complete bank. Beginning at the top, this level comprises first a strip of micarta 5, which is just below the plate I. Next below the insulation 5 comes a row of spaced contacts 6, as shown in Fig.

last layer of the level is a strip of micarta insulation 9, which is identical with strip 5.

As stated above, all the levels are the same and hence it will not be necessary to describe the rest. It may be mentioned, however, that the various levels are separated the. required distance by spacers such as It, preferably made of brass, which are of the proper thickness to secure a level spacing corresponding to, the length 0 15 the vertical steps of the switch wipers.

It will be appreciated now that since the fillers such as l0 and II are of the same thickness as the contacts such as 6 and 8, the intro duction of these fillers provides a level surface in each contact row. The wipers ride over these level surfaces with very little friction, and it is found in practice that six sets of wipers can easily be handled by the standard restoring spring and driving magnet.

The invention has incidental advantages in addition to its main object of reducing the wiper friction. The elimination of the recesses between adjacent contacts tends to prevent the accumulation of dust and dirt and consequently the newfbanks. need to be cleaned less frequently than the old. The danger of short circuiting adjacent bank contacts by wipers which have become somewhat worn is also greatly reduced. All these advantages are secured at a very small increase in cost and consequently the new bank is adapted for general use as well as for the particular use for which it was designed.

The invention having been described, that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

What is claimed is:

1. In a. switch bank, a row of spaced contacts having fiat surfaces near their ends adapted to beiengaged by a switch wiper, and a comb-shaped filler having teeth lying in the spaces between the ends of adjacent contacts, said teeth being of the same width as said spaces and the same thickness as said contacts, whereby the contacts and the fillerteeth cooperate to form a level surface.

2. In a switch bank, a row of contacts, strips of insulating material, means clamping said row of contacts between said strips, and a combshaped filler of insulating material having teeth which lie in the spaces between the ends of said contacts, the ends of said teeth being also clamped between said strips to hold the filler in place.

3. In a switch bank, a contact level comprising two rows of spaced contacts, a strip of insulating material separating said rows, and two fillers located on opposite sides of said strip and in the plane of said rows, respectively, each filler having comb-like projections interspersed between the contacts of the associated row.

RALPH W. WAGNER. 

